Although the use of highly active anti-retroviral therapy (HAART) has enhanced both the longevity and quality of life for HIV-infected individuals by controlling viral replication, financial and logistic drawbacks as well as clinical side effects and the development of drug resistance limits its worldwide use. Subsequently, the development of a safe yet effective vaccine for HIV remains the long term goal for both scientific and political communities worldwide. In light of this observation, the overall objective of this research is to develop a vaccine against HIV that combines the superior and long-lived immunity of a live-attenuated virus (LAV) with the safety of a nonreplicating particulate antigen to generate a novel, acutely-propagating chimeric particle (PCP) vaccine. These chimeric particles contain a replicating VEE/SHIV genome and are capable of infecting susceptible cells bearing hCD4/hCCR5, undergoing cytoplasmic replication, genomic RNA encapsidation, assembly, and particle release. The VEE-SHIV PCP does not contain the HIV LTRs or integrase therefore increasing the general safety of the vaccine. Due to the replicative nature of these particles, lentiviral proteins will be expressed for an extended period of time in vaccinated individuals thus inducing a more comprehensive immune response compared to nonreplicating antigens. Furthermore, the chimeric particle has an inherent safety feature;the VEE replicase machinery is sensitive to interferon thus limiting the replication until the immune response to the lentiviral proteins clears the virus. Another advantage of the VEE-SHIV PCP vaccine compared to LAV is that lentiviral structural proteins are combined with the replicase machinery from VEE, thus eliminating replication restrictions seen with wild-type lentiviruses in murine cells. Therefore, unlike wild-type lentiviruses, the VEE-SHIV PCP is infectious in the presence or absence of particle maturation and can efficiently replicate in murine cells without limitation. The main objectives of this proposal are to: 1) vaccinate hCD4/hCCR5 transgenic (hCD4/R5 Tg) and BALB/c Rag2-/-, c-/- mice reconstituted with human hematopoietic stem cells from human fetal liver (huDKO) with purified chimeric particles and DNA expressing the VEE-SHIV PCP, 2) demonstrate replication of the VEE-SHIV PCP, 3) assess safety, and 4) evaluate the immunogenicity of the PCP vaccine in hCD4/R5 Tg and huDKO mouse models. Overall, the propagating chimeric particle vaccine strategy is expected to be a safe alternative to live-attenuated vaccines in the quest for a safe, yet effective vaccine against HIV-1/AIDS. PUBLIC HEALTH RELEVANCE: Although the immunity induced by live-attenuated virus is the gold standard for HIV-1 vaccine development, safety concerns preclude their use in humans. Therefore, a VEE-SHIV propagating chimeric particle (PCP) vaccine is proposed as a safe alternative to live-attenuated virus. This prototype chimeric particle vaccine contains lentiviral structural proteins to elicit HIV-specific immunity, and the replicase machinery of VEE to permit replication in BALB/c transgenic hCD4/hCCR5 and BALB/c Rag2-/-, c-/- mice reconstituted with human hematopoietic stem cells from human fetal liver (huDKO) mouse models of HIV infection described in this application, as well as humans and non-human primates.